Comparative study of three structurally related acid polyelectrolytes as carriers of basic drugs: Carbomer, Eudragit L 100 and Eudragit S 100

Abstract

A detailed description of equilibrium and drug release properties of aqueous dispersions of complexes of model basic drugs (D) with three structurally related acid polyelectrolytes (PE) is reported. Thus, equilibrium properties of dispersions of polymetacrylates Eudragit L 100, and Eudragit S 100, neutralized with increasing proportions of Lidocaine, Metoclopramide and Atenolol, were compared with those of Carbomer that were previously reported. The proportions of PE condensed (RCOO-DH+) and free species (D and DH+) were determined on PE-Lidocaine and PE-Metoclopramide systems. Affinity constants for ionic pair formation (Kip) were calculated as a function of D loading. In agreement with the high degree of counterionic condensation observed, the three (PE-D) complexes placed on Franz type cells released D at slow rates as water was the receptor medium. Rates increased over 3 times as water was replaced by 0.9% NaCl solution. Similar average of Korsmeyer exponent n (0.61 (water) and 0.69 (NaCl)) were found in both media. The overall kinetic behavior suggests that, under the conditions assayed, the dissociation of RCOO-DH+ is the factor that controls releasing rates. Structure related properties of the PE-D systems were identified in order to expand their potential uses as drug carriers.